Definition
ChEBI: A benzothiadiazine that is 1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide substituted by an isopropyl group at position 3.
Potential Exposure
A potential danger to those involved
in the manufacture, formulation or application of this selective
postemergent thiadiazine herbicide.
First aid
If this chemical gets into the eyes, remove any
contact lenses at once and irrigate immediately for at least
15 minutes, occasionally lifting upper and lower lids. Seek
medical attention immediately. If this chemical contacts the
skin, remove contaminated clothing and wash immediately
with soap and water. Seek medical attention immediately.
If this chemical has been inhaled, remove from exposure,
begin rescue breathing (using universal precautions, including
resuscitation mask) if breathing has stopped and CPR if
heart action has stopped. Transfer promptly to a medical
facility. When this chemical has been swallowed, get medical
attention. Give large quantities of water and induce
vomiting. Do not make an unconscious person vomit.
Shipping
UN2588 Pesticides, solid, toxic, Hazard Class:
6.1; Labels: 6.1—Poisonous materials, Technical Name
Required.
Incompatibilities
Keep away from flammable materials,
heat and flame. Risk of fire and explosion if formulations
contain flammable/explosive solvents.
Description
Bentazon is unique under these herbicides
because it is the only compound that bears a sulfonyl
group. A puzzle that is not solved yet is that bentazone
is an excellent herbicide but has a very low pI50-value.
Chemical Properties
Bentazon is a colorless to white crystalline
powder.
Waste Disposal
In accordance with
40CFR165, follow recommendations for the disposal of
pesticides and pesticide containers. Must be disposed properly
by following package label directions or by contacting
your local or federal environmental control agency, or by
contacting your regional EPA office.
Production Methods
Bentazone is synthesised through a multi-step chemical process that begins with the preparation of isopropylaminosulfonyl chloride, formed by reacting isopropylamine hydrochloride with sulfonyl chloride in acetonitrile under reflux. Separately, O-aminobenzoic acid methyl ester is prepared from phthalic anhydride via a series of reactions involving aqueous ammonia, sodium hydroxide, and methanol. These two intermediates are then combined: isopropylaminosulfonyl chloride is reacted with methyl anthranilate in toluene, using ammonia or an organic base to form N-isopropylamine sulfonylmethyl anthranilate. The pH is carefully controlled and the mixture is cooled to improve product quality. Finally, cyclisation is carried out in sodium methoxide solution at 60–65 DegC for 30 minutes, followed by acidification to yield bentazone.
Agricultural Uses
Selective post-emergent herbicide: A post-emergence herbicide used to control broadleaf
weeds in crops such as beans, corn, mint, soybeans,
rice, and peanuts. All products formerly marketed in the
U.S. contain the sodium salt of bentazon as the active ingredient, referred to as sodium bentazon. Also used in
selective post-emergent control of broadlelaf weeds and
sedges in alfalfa, asparagus, cereals, clover, digitalis, dry
peas, flax, garlic, grasses, green lima beans, mint, onions,
potatoes, snap beans for seed, sorghum, soybeans and sugarcane.
Not currently registered in the U.S. It is reported to
be used in most European countries.
Trade name
ASAGIO®; BAS 351-H®; BASAGRAN®;
BENDIOXIDE®; BENTA®; BLAST®; ENTRY®;
LADDOK®; LEADER®; PLEDGE®; STORM®
Mechanism of action
Selective action, absorbed by foliage with very little translocation. Inhibits photosynthesis (photosystem II).
Environmental Fate
Soil. Under aerobic conditions, bentazone was reported to degrade to 6- and 8-hydrox ybentazone compounds. In addition, anthranilic acid and isopropylamide were reported
as soil hydrolysis products (Otto et al., 1978). Persistence in soil is less than 6 weeks
(Hartley and Kidd, 1987). Bentazone is readily adsorbed onto organic carbon and therefore,
is not expected to leach to groundwater (Abernathy and Wax, 1973). The dissipation half life of bentazone in field soil is 5 days (Ross et al., 1989).
Plant. Undergoes hydroxylation of the aromatic ring and subsequent conju-gation in
plants (Otto et al., 1978; Hartley and Kidd, 1987) forming 6- and 8-hydroxybentazone
compounds (Otto et al., 1978). The half-life in and/or on plants is 2–3 days (
Photolytic. Humburg et al. (1989) reported that 30% degradation of bentazone on glass
plates occurred when exposed to UV light (λ = 200–400 nm); however, no photoproduct(s)
were reported. The natural sunlight and simulated sunlight irradiation of
Chiron et al. (1995) investigated the photodegradation of bentazone (20 μg/L) in
distilled water and Ebro River water using an xenon arc irradiation. In distilled water,
bentazone completely disappeared after 16 hours of irradiation. Photodegradation appeared
to follow pseudo-first-order kinetics with a half-life of about 2.5 hours. The presence of
humic substances (4 mg/L) increased the rate of photodegradation and the disappearance
of bentazone was achieved in 8 hours. No significant breakdown photoproducts were
identified.
Metabolic pathway
14C-Bentazon degrades in soils under conventional
tillage and no-tillage (3-18 years) with varying
histories of bentazon application. The half-life for
bentazon degradation ranges from 4.6 to 49.5 days;
half-lives for some no-tillage soils with the longest
histories of application are lower than those of
conventional tillage soils. Half-lives for soils with no
bentazon history are 3-11 times higher than the half-
lives of those previously exposed to bentazon. N-
Methylbentazon is the most consistently observed
metabolite. The other metabolites identified in soils
result from hydroxylation on the phenyl ring and the
cleavage of the benzothiadiazine ring, yielding 6- and
8-hydroxybentazons and anthranilic acid via
2-amino-N-isopropylbenzamide.
storage
Color Code—Blue: Health Hazard/Poison: Storein a secure poison location. Store in tightly closed containers in a cool, well-ventilated area away from flammablematerials, sources of heat and fire.
